1. Field of the Disclosure
This disclosure relates in general to methods of synthesis of fluorinated olefins.
2. Description of the Related Art
The fluorocarbon industry has been working for the past few decades to find replacement refrigerants for the ozone depleting chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) being phased out as a result of the Montreal Protocol. The solution for many applications has been the commercialization of hydrofluorocarbon (HFC) compounds for use as refrigerants, solvents, fire extinguishing agents, blowing agents and propellants. These new compounds, such as HFC refrigerants, HFC-134a and HFC-125 being the most widely used at this time, have zero ozone depletion potential and thus are not affected by the current regulatory phase-out as a result of the Montreal Protocol.
In addition to ozone depleting concerns, global warming is another environmental concern in many of these applications. Thus, there is a need for compositions that meet both low ozone depletion standards as well as having low global warming potentials. Certain hydrofluoroolefins are believed to meet both goals. Thus there is a need for manufacturing processes that provide halogenated hydrocarbons and fluoroolefins that contain no chlorine that also have a low global warming potential.
HFC-1234yf (CF3CF═CH2) and HFC-1234ze (CF3CH═CHF), both having zero ozone depletion and low global warming potential, have been identified as potential refrigerants. U.S. Patent Publication No. 2006/0106263 A1 discloses the production of HFC-1234yf by a catalytic vapor phase dehydrofluorination of CF3CF2CH3 or CF3CHFCH2F, and of HFC-1234ze (mixture of E- and Z-isomers) by a catalytic vapor phase dehydrofluorination of CF3CH2CHF2.
The catalytic dehydrofluorination of hydrofluorocarbons to produce hydrofluoroolefins is ordinarily carried out in the vapor phase using a dehydrofluorination catalyst. Vapor phase dehydrofluorination catalysts are well known in the art. These catalysts include, but are not limited to, alumina, aluminum fluoride, fluorided alumina, metal compounds on aluminum fluoride, metal compounds on fluorided alumina; chromium oxides, fluorided chromium oxides, and cubic chromium trifluoride; oxides, fluorides, and oxyfluorides of magnesium, zinc and mixtures of magnesium and zinc and/or aluminum; lanthanum oxide and fluorided lanthanum oxide; carbon, acid-washed carbon, activated carbon, three dimensional matrix carbonaceous materials; and metal compounds supported on carbon. The metal compounds are oxides, fluorides, and oxyfluorides of at least one metal selected from the group consisting of sodium, potassium, rubidium, cesium, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, chromium, iron, cobalt, rhodium, nickel, copper, zinc, and mixtures thereof. In the alternative, dehydrofluorinations can be carried out in the liquid phase through reaction with aqueous or alcohol solutions of caustic, such as potassium hydroxide, or sodium hydroxide.
Catalytic dehydrofluorination of HFC-245fa in general produces a mixture of both the E-isomer as well as the Z-isomer of HFC-1234ze. Depending on the particular catalyst chosen, the amount of the Z-isomer can vary between 15 to 23%. Dehydrofluorination in the liquid phase using aqueous solutions of caustic or other strong bases also produces mixture of both isomers. Although the ratio of the two isomers can be shifted somewhat by temperature, about 13-15% of the Z-isomer is typically formed. As the E-isomer is the most useful for refrigeration applications, after separation of the E-isomer from the Z-isomer, the Z-isomer is typically either isomerized to the E-isomer in a separate step, or converted back to 245fa through addition of hydrogen fluoride. Both alternatives require additional steps which add cost.
There is a continuing need for more selective and efficient manufacturing processes for the production of HFC-1234ze and HFC-1234yf.